For example, a particle beam irradiation method is currently used in cancer treatment. The particle beam irradiation method includes a method called broad beam method. In the broad beam method, a beam diameter is expanded to a size equal to or larger than the size of an affected part by a method called a wobbler method or a double scattering method. Further, in the broad beam method, a collimator limits an irradiation area to direct the beam in accordance with the shape of the affected part. However, the broad beam method cannot achieve three-dimensional exact matching of the beam to the affected part shape, and there is a limit on reduction in adverse effect on normal cells around the affected part.
In light of this, there has been developed a three-dimensional (3D) scanning irradiation method. In the 3D scanning irradiation method, irradiation is performed in such a manner as to three-dimensionally fill an affected part without a collimator. The particle beam treatment by this three-dimensional scanning irradiation method is performed in the following first to three steps.
In the first step, computed tomography (hereinafter, abbreviated as “CT”) is performed for the purpose of making a treatment plan. A CT image obtained by the CT is used not only for making the treatment plan, but also for creating a reference image for positioning of the patient during treatment. The first step is generally performed on a previous day of the treatment day.
In the second step, the position of the patient is set. Specifically, the patient is placed on a treatment bed, and a mark formed on the surface of a fixing tool for fixing the patient is adjusted to the irradiation center. In this state, X-ray fluoroscopy is performed. Then, a fluoroscopic image obtained by the X-ray fluoroscopy and the reference image obtained from the CT image in advance are compared to calculate a positional deviation amount. Subsequently, the deviation amount is set to the treatment bed so as to make the fluoroscopic image and reference image agree with each other.
In the third step, irradiation of a particle beam is performed. Specifically, individual devices of an irradiation system are put into an irradiation enabled state after the setting of the patient's position, and then irradiation is started. The three-dimensional scanning irradiation method is a method that irradiates an affected part according to the treatment plan designed in advance based on the CT image.
However, according to the above procedure, the first step is conducted before the treatment day, so that the position of an affected part and the position of normal tissue may change depending on the conditions of body gas, digests, and excrement in the patient's body. In this case, even when the patient's position is reset to the treatment bed, there remains a problem concerning reliability of reproducibility of the position.
Further, in the second step, the treatment bed needs to be moved after the X-ray photography, so that a high requirement is placed on the positional accuracy of the treatment bed, with the result that daily (usually, in the morning before the start of the treatment) QA (Quality Assurance) test takes time. Further, after the treatment bed is moved, X-ray photography needs to be performed again in order to confirm that the set position is correct. As a result, it takes time to perform device setting for X-ray photography, and exposure dose of the patient is increased.